Aquatic Mammals 2004, 30(2), 315-326, DOI 10.1578/AM.30.2.2004.315
Anatomical Description of an Infant Bottlenose Dolphin (Tursiops
truncatus) Brain from Magnetic Resonance Images
Lori Marino,1 Keith Sudheimer,2 D. Ann Pabst,3 William A. McLellan,3
Saima Arshad,1 Greeshma Naini,1 and John I. Johnson2,4
Neuroscience and Behavioral Biology Program, Emory University, Atlanta, GA, USA
2
Department of Radiology, Michigan State University, East Lansing, MI, USA
3
Biological Sciences and Center for Marine Science,
University of North Carolina at Wilmington, Wilmington, NC, USA
4
Neuroscience Program, Michigan State University, East Lansing, MI, USA
1
Abstract
Cetacean brains are among the least studied mammalian brains because of the formidable histological preparations of such relatively rare and large
specimens. Although the bottlenose dolphin,
Tursiops truncatus, has been the most extensively
studied cetacean species, there have been relatively
few studies of the brain of the infant bottlenose
dolphin. In this study, we present the first magnetic resonance imaging (MRI)-based study of the
brain of an infant bottlenose dolphin. Magnetic
resonance images in the coronal plane were originally acquired and used to digitally generate a set
of resectioned virtual images in orthogonal planes.
A sequential set of images in all three planes was
anatomically labeled and reveals major neuroanatomical features. Some of the distinctive features
of cetacean brains are already evident in the infant
bottlenose dolphin brain, while other features may
represent differences that deserve further study.
Key Words: bottlenose dolphin, Tursiops truncatus, brain, neuroanatomy, magnetic resonance
imaging
Introduction
Cetacean brains have been of interest to mammalogists and comparative neuroanatomists for decades
because cetaceans are highly divergent from other
mammals, and their unusual brains represent a
striking blend of conservative and highly derived
characteristics (Glezer et al., 1988; Manger et al.,
1998; Ridgway, 1986, 1990). For this reason, the
study of cetacean brains, particularly in comparison with the brains of primates and other largebrained mammals, is important for a complete
understanding of the range of forms mammalian
brain evolution can take. Non-adult brains offer
© 2004 EAAM
insight into the developmental patterns that may
be recruited for evolutionary change.
There are several published studies on adult
brains from the cetacean suborder Odontoceti
(toothed whales, dolphins, and porpoises). These
include Kojima’s (1951) description of the sperm
whale (Physeter macrocephalus) brain and MRIbased descriptions of the adult bottlenose dolphin
(Tursiops truncatus) brain (Marino et al., 2001c),
the adult beluga whale (Delphinapterus leucas)
brain (Marino et al., 2001b), and the adult common
dolphin (Delphinus delphis) brain (Marino et al.,
2002). Several studies document the differences
between odontocete and other mammalian brains
at the level of cortical cytoarchitecture and immunohistochemistry (Garey & Leuba, 1986; Garey
et al.. 1985; Glezer & Morgane, 1990; Glezer et
al., 1990, 1992a, 1992b, 1998; Hof et al., 1992,
1995), cortical surface morphology (Haug, 1987;
Jacobs et al., 1979; Morgane et al., 1980), and
noncortical structures and features (Glezer et al.,
1995; Tarpley & Ridgway, 1994). There also have
been quantitative descriptions of the brains of
the Ganges River dolphin (Platanista gangetica)
(Kamiya & Pirlot, 1980) and the franciscana dolphin (Pontoporia blainvillei) (Schwerdtfeger et al.,
1984). The most comprehension description of the
adult cetacean brain in comparison to the brains of
other marine mammal species is the recent review
by Oelschlager & Oelschlager (2002).
Relatively few papers have focused on the
developmental features of cetacean brains. Many
of these involve descriptions of postnatal growth
patterns for the whole brain, rather than for
more specific morphological features (Marino,
1995—bottlenose dolphin; Marino, 1998—
Franciscana dolphin; Marino, 1999—harbor porpoise [Phocoena phocoena] and Pacific whitesided dolphin [Lagenorhynchus obliquidens];
Pirlot & Kamiya, 1975—franciscana dolphin and
316
Marino et al.
striped dolphin [Stenella coeruleoalba]; Ridgway
& Brownson, 1984—bottlenose dolphin, killer
whale [Orcinus orca], and common dolphin).
Other studies have primarily focused on prenatal
brain development (Holzmann, 1991—Narwhal
[Monodon monoceros]; Kamiya & Pirlot, 1974—
striped dolphin; Marino et al., 2001a—common
dolphin; Oelschlager & Kemp, 1998—sperm
whale; Buhl & Oelschlager, 1988—harbor porpoise (Phocoena phocoena); Wanke, 1990—spotted dolphin [Stenella attenuata]).
Until the present study there have been no
detailed descriptions of the overall morphology of
the bottlenose dolphin brain during early infancy.
In this study, we present the first morphological
description of an infant bottlenose dolphin brain
based upon magnetic resonance imaging (MRI) in
all three spatial planes. In addition, these images
are compared with MRI scans of the brain of an
adult bottlenose dolphin from a previously published study. The MRI offers a means of observing
the internal structure of these large brains where
traditional methods of embedding, sectioning,
staining, mounting, and microscopic examination are not practical. Furthermore, MRI offers
the opportunity to observe internal structures in
their precise anatomical positions because the
fixed whole brain is kept intact during the scanning therefore minimizing the spatial distortions
associated with many histology methods.
Materials and Methods
Specimen
The specimen was the postmortem brain of an
infant male bottlenose dolphin (Tursiops truncatus)
that stranded deceased on 20 July 2000 on Virginia
Beach (Field#VMSM20001031). The carcass
was in fresh condition (Smithsonian Institution
Condition Code 2; Geraci & Loundsbury, 1993)
and was frozen immediately for later necropsy.
The dolphin was thawed in 25° C water on 20
January 2001, and during necropsy, the brain was
extracted from the skull, weighed, and placed in
10% neutral buffered formalin. The brain mass at
necropsy was 766 g. The anterior-posterior length
of the brain was 132 mm. The bitemporal width
was 155 mm. The height of the brain was 96 mm.
Total body length of the dolphin was 127 cm,
and total body weight was 29.2 kg. Body length
is consistent with an estimated postnatal age of
less than six months, but not a newborn (Harrison,
1969; Harrison et al., 1972; Mead & Potter, 1990;
Perrin & Reilly, 1984; Read et al., 1993; Sergeant
et al., 1973). The specimen did not have fetal
folds, but possessed a healed umbilicus, relatively
flexible flukes, and five to six erupted upper teeth
on both tooth rows of the rostrum. Information
on patterns of abundance and distribution for
neonates in the same nearshore waters as the
present specimen was obtained from Barco et al.
(1999). Taken together, the body weight and length
and other physical features lead us to estimate that
the postnatal age of the present specimen was two
to three months.
MRI Protocol
Magnetic resonance (MR) images of the entire
brain were acquired in the coronal plane with a 1.5
T Philips NT scanner (Philips Medical System,
The Netherlands) at Emory University School of
Medicine. Imaging protocol parameters were slice
thickness = 2 mm, slice interval = 0 mm, TR =
3,000 msec, TE = 13 msec, field of view = 160
mm, and matrix = 256 X 256 pixels. The specimen was scanned with the ventral side down in
the human head coil. Approximate scan time for
the coronal series was 20 min. The period of time
between brain extraction and scanning was 77
days. Whereas the clarity of MRI scans and the
integrity of brain tissue can potentially be disrupted by freezing and thawing, we saw no evidence of any detrimental effects on the tissue or
scans in the present specimen.
Three-Dimensional Reconstruction and
Reformatting
A computer-generated 3D model was created
using the software program VoxelView (Vital
Images, Inc.) at the Laser Scanning Microscopy
Laboratory at Michigan State University. The 3D
rendered model was then digitally resectioned in
orthogonal planes to produce corresponding virtual section series in the horizontal (145 0.6-mm
thick virtual sections) and sagittal (255 0.5-mm
thick virtual sections) planes.
Volume Measurements
Whole brain volume was measured manually with the image analysis software program
Scion IMAGE for Windows (PC version of NIH
IMAGE), using manually defined areas from successive slices that were integrated to arrive at a
volume estimate. The entire volumetric estimate
was converted to weight units by multiplying the
volume by the specific gravity of brain tissue or
1.036 g/cm3 (Stephan et al., 1981).
Anatomical Labeling and Nomenclature
All identifiable brain structures of the specimen
were labeled in the originally acquired coronal
plane images, as well as in the images from the
virtual sectioned brain in the sagittal and horizontal planes. The MR images of the dolphin brain
were compared with the published photographs
and illustrations of the adult bottlenose dolphin
Infant Bottlenose Dolphin Brain
brain from Morgane et al. (1980), as well as published neuroanatomical atlases based on MR scans
of an adult bottlenose dolphin brain (Marino et al.,
2001c). Nomenclature is based upon Marino et al.
(2001c) and Morgane et al. (1980). Additionally,
scans also were compared with several complete
alternate series of sections of the adult bottlenose
dolphin brain, which were stained, respectively,
for cell bodies (Nissl method) and for myelinated
fibers in the same three orthogonal planes (coronal or transverse, sagittal, and horizontal). These
stained section series are from the YakovlevHaleem Collection at the National Museum of
Health and Medicine and the Welker Collection at
the University of Wisconsin at Madison.
Results
Volumetric Measurements
The measured whole brain volume of the specimen
from MR scans was 705.3 cc. When converted to
weight by multiplication with the value of the specific gravity of water, the estimate of whole brain
weight from the MR images was 730.69 g. The
MRI-based value is similar to the measured brain
weight of 766 g at the time of necropsy. A previously published value for average whole brain
volume in newborn bottlenose dolphins was 713.0
cc (Marino, 1995). Average adult brain weight for
bottlenose dolphins is 1,824 g (Marino, 1998). The
estimated brain weight for the present specimen is
40.1% of the published average adult brain weight.
This is consistent with Ridgway & Brownson
(1984) who found that neonatal brain weight averaged 42.5% of the average adult brain weight in
bottlenose dolphins. The present estimated brain
weight is also consistent with the estimated age
317
of the specimen and within the published range
of brain weights 676-750 g for infant bottlenose
dolphins of similar age (Marino, 1995).
Anatomical Description
Figures 1a and b shows a photograph of the specimen and an image of a reconstructed adult bottlenose dolphin brain from MR scans from Marino
et al. (2001c). Figure 1, in general, shows that
the infant bottlenose dolphin brain resembles the
adult in overall shape and structure.
Figure 2 (a-h) displays a posterior-to-anterior
sequence of originally acquired 2.0 mm-thick
coronal MR brain sections at 10-mm intervals
and a labeled schematic illustration of each section. Figure 3 (a-h) displays a dorsal-to-ventral
sequence of reconstructed “virtual” 0.6-mm thick
horizontal sections at 6-mm intervals and a labeled
schematic illustration of each section. Figure 4 (ah) displays a midline-to-lateral sequence of reconstructed 0.5-mm thick “virtual” sagittal sections
through the left hemisphere at 3-mm intervals and
a labeled schematic illustration of each section.
The MR scans reveal, not unexpectedly, that the
internal structure of the infant bottlenose dolphin
brain resembles that of the adult bottlenose dolphin brain. Some of the specific features unique to
cetaceans are observable in the infant brain. Many
of these features involve the relative size of various structures and regions. The proportionately
large size of the inferior colliculus in Figures 2d,
3e and f, and 4c and d; the thalamus in Figures
2f, 3c, and 4d-f; the cerebellum in Figures 2b
and c, 3f and g, and 4c-e; and the pons in Figures
2e, 3h, and 4b is evident. Likewise, the relatively diminutive size of the corpus callosum in
Figures 2h and 4a-c and the hippocampal region
Figure 1. (a) Photograph of the infant bottlenose dolphin brain, and (b) adult bottlenose dolphin brain reconstructed from
MRI scans
318
Marino et al.
Figure 2 (a-h). Posterior-to-anterior sequence of originally acquired 2.0-mm thick coronal MR brain sections
at 10-mm intervals and a labeled schematic illustration of each section
in Figure 2f is apparent. Furthermore, the present
specimen possesses distinctive cetacean features
regarding the spatial arrangement of subcortical
structures. For instance, in most other mammals
the cerebral peduncle lies on the ventral surface
of the midbrain. In the present specimen (see
Figure 2f) and other cetacean species (Marino
et al., 2002; pers. obs.), the cerebral peduncle is
located high on the lateral surface of the ventral
midbrain.
One of the ways in which the present specimen
appears different from the adult bottlenose dolphin
brain is in the degree of myelination of the thalamo-cortical radiations. As evident in Figures 2 c-h
and 3 b-e, the degree of branching of myelinated
fibers (which appear dark grey) does not seem to be
as extensive as in the adult bottlenose dolphin brain
(Marino et al., 2001c). Furthermore, those radiations that are most visible (of the darkest shade of
grey) appear to be concentrated in the dorsal medial
gyri of the parietal lobes. This observation must be
interpreted with caution, however, because it is not
clear whether this pattern is due to limits in contrast
and spatial resolution of the MR scans or whether it
represents a real difference in myelination patterns
between the infant and adult bottlenose dolphin.
Further analyses of both MR scanned and histologically prepared infant bottlenose dolphin brains
are required to differentiate between these two
possibilities.
Infant Bottlenose Dolphin Brain
© 2004 EAAM
319
320
Marino et al.
Figure 3 (a-h). Dorsal-to-ventral sequence of reconstructed “virtual” 0.6-mm thick horizontal sections at
6-mm intervals and a labeled schematic illustration of each section
Infant Bottlenose Dolphin Brain
321
322
Marino et al.
Figure 4 (a-h). Midline-to-lateral sequence of reconstructed 0.5-mm thick “virtual” sagittal sections through
the left hemisphere at 3-mm intervals and a labeled schematic illustration of each section
Infant Bottlenose Dolphin Brain
323
324
Marino et al.
Discussion
The present study displays anatomically labeled
MR images of a postmortem infant bottlenose
dolphin brain. The findings reveal that the infant
brain is very similar in many morphological
respects to that of the adult bottlenose dolphin
brain and displays a number of features unique to
cetacean brains. These include the gross morphological characteristics, the relative size proportions of various structures, and the peculiar spatial
arrangement of some of the structures. There is
an intriguing suggestion that myelination patterns
in the infant brain may be different from those in
the adult brain. Further quantitative analyses will
determine whether this observation is accurate
and will allow for these patterns to be described
in more detail.
This study represents one of a handful of studies
of early brain development in the bottlenose dolphin. The study of early postnatal (and prenatal)
cetacean brain development has been constrained
by the lack of data. This situation can be resolved
by using an MRI to analyze the numerous postmortem specimens available in museums and similar facilities. The present study demonstrates that
MR images of early postnatal dolphin brains can
be obtained to formulate a database on the normative range of morphometric values for whole
brains and substructures in cetaceans. The MRI
also allows for the preservation of spatial aspects
of internal structures and their relationship to one
another. This enables accurate three-dimensional
reconstruction, which then offers the flexibility
to view any part of the brain from any angle and
in any plane of sectioning while maintaining the
intactness of the specimen. This study is part of a
larger effort towards the study of developmental
morphometrics in cetaceans as a way to elucidate
not only ontogeny but potential evolutionary patterns as well.
Comparative analyses of neuroanatomical
developmental patterns in and among cetaceans
and other mammals are critical for elucidating
the history of phylogenetic divergence among
cetacean species and between cetaceans and other
mammals. Studies of cetacean brain development
provide valuable data that will assist efforts to
reconstruct the evolutionary history of cetaceans
since their divergence from terrestrial ancestors.
Acknowledgments
Special thanks are given to Dr. Hui Mao for his
assistance and advice during the MRI scanning.
We thank Joanne Whallon for use of the VoxelView
programs and Silicon Graphics, Inc. workstations
at the Laser Scanning Microscopy Laboratory
Infant Bottlenose Dolphin Brain
at Michigan State University. We also thank W.
Welker, A. Noe, and A. J. Fobbs for use of stained
sections in the Wisconsin and Yakovlev-Haleem
Collections, and Patsy Bryan for her excellent illustrations. The dolphin specimen was collected by
the University of North Carolina at Wilmington’s
Marine Mammal Stranding Program under a Letter
of Authorization from the National Marine Fisheries
Service. This study was supported by an Emory
University Research Committee Award and NSF
Division of Integrative Biology and Neuroscience
grants 9812712, 9814911, and 9814912.
Literature Cited
Barco, S. G., Swingle, W. M., McLellan, W. A., Harris,
R. N., & Pabst, D. A. (1999). Local abundance and distribution of bottlenose dolphins (Tursiops truncatus) in
the nearshore waters of Virginia Beach, Virginia. Marine
Mammal Science, 15(2), 394-408.
Buhl, E. H., & Oelschlager, H. A. (1988). Morphogenesis
of the brain in the harbour porpoise. Journal of
Comparative Neurology, 277, 109-125.
Garey, L. J., & Leuba, G. (1986). A quantitative study of
neuronal and glial numerical density in the visual cortex
of the bottlenose dolphin: Evidence for a specialized
subarea and changes with age. Journal of Comparative
Neurology, 247, 491-496.
Garey, L. J., Winkelman, E., & Brauer, K. (1985). Golgi
and Nissl studies of the visual cortex of the bottlenose
dolphin. Journal of Comparative Neurology, 240, 305321.
Geraci, J. R., & Lounsbury, V. J. (1993). Marine mammals
ashore: A field guide for strandings. Galveston: Texas
A&M University Sea Grant College Program.
Glezer, I. I., & Morgane, P. J. (1990). Ultrastructure of
synapses and Golgi analysis of neurons in neocortex of
the lateral gyrus (visual cortex) of the dolphin and pilot
whale. Brain Research Bulletin, 24, 401-427.
Glezer, I. I., Hof, P. R., & Morgane, P. J. (1992b). Calretininimmunoreactive neurons in the primary visual cortex of
dolphin and human brains. Brain Research, 595, 181188.
Glezer, I. I., Hof, P. R., & Morgane, P. J. (1995).
Cytoarchitectonics and immunocytochemistry of
the inferior colliculus of midbrain in cetaceans. The
Federation of American Societies for Experimental
Biology Journal, 9, A247-A247.
Glezer, I. I., Hof, P. R., & Morgane, P. J. (1998). Comparative
analysis of calcium-binding protein-immunoreactive
neuronal populations in the auditory and visual systems
of the bottlenose dolphin (Tursiops truncatus) and the
macaque monkey (Macaca fascicularis). Journal of
Chemical Neurology, 15, 203-237.
Glezer, I. I., Jacobs, M., & Morgane, P. J. (1988).
Implications of the “initial brain” concept for brain evolution in cetacea. Behavioral and Brain Sciences, 11,
75-116.
325
Glezer, I. I., Morgane, P. J., & Leranth, C. (1990).
Immunohistochemistry of neurotransmitters in visual
cortex of several toothed whales: Light and electron
microscopic study. In J. A. Thomas & R. A. Kastelein
(Eds.), Sensory abilities of cetaceans: Laboratory and
field evidence (pp. 39-60). New York: Plenum Press.
Glezer, I. I., Hof, P. R., Leranth, C., & Morgane P. J. (1992a).
Morphological and histological features of odontocete
visual neocortex: Immunocytochemical analysis of
pyramidal and nonpyramidal populations of neurons. In
J. A. Thomas, R. A. Kastelein, & A. Y. Supin (Eds.),
Marine mammal sensory systems (pp. 1-38). New York:
Plenum Press.
Harrison, R. J. (1969). Reproduction and reproductive
organs. In H. T. Anderson (Ed.), The biology of marine
mammals (pp. 253-342). New York: Academic Press.
Harrison, R. J., Brownell, R. L., & Boise, R. C. (1972).
Reproduction and gonadal appearances in some
odontocetes. In R. J. Harrison (Ed.), Functional anatomy of marine mammals. New York: Academic Press.
451 pp.
Haug, H. (1987). Brain sizes, surfaces and neuronal sizes
of the cortex cerebri: A stereological investigation of
man and his variability and a comparison with some
mammals (primates, whales, marsupialia, insectivores
and one elephant). American Journal of Anatomy, 180,
126-142.
Hof, P. R., Glezer, I. I., Archin, N., Janssen, W. G., Morgane,
P. J., & Morrison, J. H. (1992). The primary auditory
cortex in cetacean and human brain: A comparative
analysis of neurofilament protein-containing pyramidal
neurons. Neuroscience Letters, 146, 91-95.
Hof, P. R., Glezer, I. I., Revishchin, A. V., Bouras, C.,
Charnay, Y., & Morgane, P. J. (1995). Distribution of
dopaminergic fibers and neurons in visual and auditory
cortices of the harbor porpoise and pilot whale. Brain
Research Bulletin, 36, 275-284.
Holzmann, T. (1991). Morphologie and microscopische
anatomie des Gehirns beim fetalen Narwal, Monodon
monoceros. Thesis, Faculty of Human Medicine,
University of Frankfurt.
Jacobs, M. S., McFarland, W. L., & Morgane, P. J. (1979).
The anatomy of the brain of the bottlenose dolphin
(Tursiops truncatus). Rhinic lobe (rhinencephalon): The
archicortex. Brain Research Bulletin, 4, 1-108.
Kamiya, T., & Pirlot, P. (1974). Brain morphogenesis in
Stenella coeruleoalba. Scientific Reports of the Whales
Research Institute Tokyo, 2, 245-253.
Kamiya, T., & Pirlot, P. (1980). Brain organization in
Platanista gangetica. Scientific Reports of the Whales
Research Institute Tokyo, 32, 105-126.
Kojima, T. (1951). On the brain of the sperm whale
(Physeter catadon L.). Scientific Reports of the Whales
Research Institute Tokyo, 6, 49-72.
Manger, P., Sum, M., Szymanski, M., Ridgway, S., &
Krubitzer, L. (1998). Modular subdivisions of dolphin
insular cortex: Does evolutionary history repeat itself?
Journal of Cognitive Neurology, 10, 153-166.
326
Marino et al.
Marino, L. (1995). Brain-behavior relationships in cetaceans and primates: Implications or the evolution of
complex intelligence. Doctoral thesis, State University
of New York at Albany. 488 pp.
Marino, L. (1998). Brain growth patterns in the
La Plata River dolphin (Pontoporia blainvillei). Aquatic
Mammals, 24(3), 111-116.
Marino, L. (1999). Brain growth in the harbor porpoise
(Phocoena phocoena) and Pacific white-sided dolphin
(Lagenorhynchus obliquidens). Journal of Mammalogy,
80(4), 1353-1360.
Marino, L., Murphy, T. L., Gozal, L., & Johnson, J. I.
(2001a). Magnetic resonance imaging and three-dimensional reconstructions of the brain of the fetal common
dolphin, Delphinus delphis. Anatomy and Embryology,
203(5), 393-402.
Marino, L., Sudheimer, K., Pabst, D. A., McLellan, W. A.,
Filsoof, D., & Johnson, J. I. (2002). Neuroanatomy of
the common dolphin (Delphinus delphis) as revealed
by magnetic resonance images (MRI). The Anatomical
Record, 268, 411-429.
Marino, L., Murphy, T. L., DeWeerd, A. L., Morris, J. A.,
Ridgway, S. H., Fobbs, A. J., Humblot, N., & Johnson,
J. I. (2001b). Anatomy and three-dimensional reconstructions of the brain of a white whale (Delphinapterus
leucas) from magnetic resonance images (MRI). The
Anatomical Record, 262, 429-439.
Marino, L., Sudheimer, K., Murphy, T. L., Davis, K. K.,
Pabst, D. A., McLellan, W. A., Rilling, J. K., & Johnson,
J. I. (2001c). Anatomy and three-dimensional reconstructions of the bottlenose dolphin (Tursiops truncatus)
brain from magnetic resonance images. The Anatomical
Record, 264, 397-414.
Mead, J. G., & Potter, C. W. (1990). Natural history of
bottlenose dolphins along the central Atlantic coast of
the United States. In S. Leatherwood & R. R. Reeves
(Eds.), The bottlenose dolphin (pp. 165-195). New York:
Academic Press.
Morgane, P. J., Jacobs, M. S., & MacFarland, W. L. (1980).
The anatomy of the brain of the bottlenose dolphin
(Tursiops truncatus): Surface configurations of the telencephalon of the bottlenose dolphin with comparative
anatomical observations in four other cetacean species.
Brain Research Bulletin, 5, 1-107.
Oelschlager, H. A., & Kemp, B. (1998). Ontogenesis of the
sperm whale brain. Journal of Comparative Neurology,
399, 210-228.
Oelschlager, H. A., & Oelschlager J. S. (2002). Brain. In
W. F. Perrin, B. Würsig, & J. G. M. Thewissen (Eds.),
Encyclopedia of marine mammals (pp. 133-158).
San Diego: Academic Press.
Perrin, W. F., & Reilly, S. B. (1984). Reproductive parameters of dolphins and small whales of the family
Delphinidae. Report of the International Whaling
Commission, 6 (Special Issue), 97-133.
Pirlot, P., & Kamiya, T. (1975). Comparison of ontogenetic
brain growth in marine and coastal dolphins. Growth,
39, 507-525.
Read, A. J., Wells, R. S., Hohn, A. A., & Scott, M. D.
(1993). Patterns of growth in wild bottlenose dolphins,
Tursiops truncatus. Journal of Zoology, London, 231,
107-123.
Ridgway, S. H. (1986). The central nervous system of the
bottlenose dolphin. In R. J. Schusterman, J. A. Thomas,
& F. G. Wood (Eds.), Dolphin cognition and behavior:
A comparative approach (pp. 31-60). Hillsdale, NJ:
Lawrance Erlbaum Associates.
Ridgway, S. H. (1990). The central nervous system of the
bottlenose dolphin. In S. Leatherwood & R. R. Reeves
(Eds.), The bottlenose dolphin (pp. 69-97). San Diego:
Academic Press.
Ridgway, S. H., & Brownson, R. H. (1984). Relative brain
sizes and cortical surface areas of odontocetes. Acta
Zoologica, 172, 149-152.
Schwerdtfeger, W. K., Oelschlager, H. A., & Stephan, H.
(1984). Quantitative neuroanatomy of the brain of the
La Plata dolphin, Pontoporia blainvillei. Anatomy and
Embryology, 170, 11-19.
Sergeant, D. E., Caldwell, D. K., & Caldwell, M. C. (1973).
Age, growth and maturity of bottlenosed dolphins
(Tursiops truncatus) from northeast Florida. Journal
of the Fisheries Research Board of Canada, 30, 10091011.
Stephan, H., Frahm, H., & Baron, G. (1981). New and
revised data on volumes of brain structures in insectivores and primates. Folia Primatologica, 25, 1-29.
Tarpley, R. L., & Ridgway, S. H. (1994). Corpus callosum size in delphinid cetaceans. Brain, Behavior, and
Evolution, 44, 156-165.
Wanke, T. (1990). Morphogenese des Gehirns heim
Schlanken Delphin Stenella attenuata (Gray, 1846).
Thesis, Faculty of Human Medicine, University of
Frankfurt am Main.